1. Field of the Invention
The present invention relates, generally, to a disk player, and more particularly, to a disk player for allocating pointers to respective frames of CD data and storing the pointers in a memory to reproduce the CD data even in a jitter environment, and methods of processing reproduced data of the disk player.
2. Description of the Related Art
In a Compact disk (CD) player, when so-called “track jumping” occurs due to an external impact causing vibration during the disk reproduction, it is important to prevent “sound discontinuity” by ensuring continuity of PCM data. Track jumping means that a light spot of a pickup unit, which reads recorded information by tracing tracks on the disk, deviates from the tracks.
FIG. 1 is a schematic of a conventional CD player. Referring to FIG. 1, a disk 1 is driven by a spindle motor 2. The recorded information of the disk 1 is read by an optical pickup unit 3. The optical pickup unit 3 comprises an object lens 5 for focusing a laser beam as an information-read-out light spot on a signal plane of the disk 1, a polarizing beam splitter 6 for changing a direction of a reflected light beam from the disk 1, and a photo detector 7 for receiving the reflected light beam. The optical pickup unit 3 is arranged to move in a radial direction. An output current signal of the optical pickup unit 3 is converted to a voltage signal by an I/V amplifier 8. The voltage signal is subjected to a waveform-shaping process in an RF equalizer circuit 9, and then, the signal is processed by a DSP circuit 10.
The DSP circuit 10 comprises a PLL asymmetry correction circuit 11, an EFM (eight-to-fourteen modulation) demodulation circuit 12, a sub-code processing circuit 13, a RAM 14, an error correction circuit 15, a de-interleave circuit 16, a spindle servo processing unit 18, and a clock signal generator 17. The PLL asymmetry correction circuit 11 corrects a deviation of the RF signal center from the amplitude center. The EFM signal demodulation circuit 12 demodulates an EFM signal, the sub-code synchronization signal SCOR, and a sub-code signal. The demodulated sub-code signal is sent through the sub-code processing circuit 13 to a microcomputer 20, which has overall control over the system. After the EFM demodulation, the PCM data is temporarily stored in the RAM 14. The error correction circuit 15 performs an error correction based on the error correction/detection parity of the PCM data. The interleave of a CIRC (cross interleave Reed-Solomon code) is released by the de-interleave circuit 16. The clock signal generator 17 generates a system clock signal based on an oscillation output of a quartz oscillator 21, so that the DSP circuit 10 can process signals based on the system clock signal.
In the RAM 14, a reproducing clock signal, which is generated by the PLL asymmetry correction circuit 11, is used as a write-in clock signal WFCK and the system clock signal is used as a read-out clock signal RFCK. The PCM data, which is processed by the DSP circuit 10, is stored in a large capacity DRAM 23 through an ESP (electric shock proof) controller 22. The PCM data, which is stored in the DRAM 23, is read by the ESP controller 22, subjected to a filtering process in a digital filter 24 and an analog process in a D/A (digital-to-analog) converter 25, and then, output as an audio signal through left and right channels.
The DRAM 23 is used to ensure continuity of PCM data to prevent the sound discontinuity when track jumping occurs due to an external impact causing vibration during the disk reproduction. When track jumping occurs, the information-read-out light spot of the optical pickup unit 3 is returned to the point just before the occurrence of track jumping and reproduction is carried out at this point, under the control of the microcomputer 20. In addition, the PCM data stored in the DRAM 23 just before the occurrence of track jumping is linked to the PCM data obtained after reproduction under the control of the ESP controller 22.
Since the sound continuity process is carried out in units of a sub-code frame, wow, which is a variation in the pitch of the music caused by, e.g., some mechanical flaw, of the spindle motor 2 is removed in the reproducing sub-code synchronization signal SCOR to maintain the sound continuity in the time axis. The ESP controller 22 further comprises a sub-code synchronization signal generation circuit for generating a sub-code synchronization signal SCOR in which the wow of the spindle motor 22 is removed, as shown in FIG. 2.
FIG. 2 is a diagram illustrating a sub-code synchronization signal generation circuit of the conventional CD player of FIG. 1. Referring to FIG. 2, a jitter counter 28 measures the value of jitter of the write-in clock signal WFCK with reference to the read-out clock signal RFCK. The write-in clock signal WFCK is a reproduced clock signal from the disk 1 and the read-out clock signal is a fixed clock signal. An inner circumference counter 29 is provided to count 98 frames of the write-in clock signal WFCK. In an addition/subtraction unit 30, the output of the inner circumference counter 29 is added to, or subtracted from, the value of jitter measured by the jitter counter 28.
The value of jitter is subtracted from the counter output corresponding to the 98 frames of the write-in clock signal WFCK, and the reproducing sub-code synchronization signal SCOR having the wow of the spindle motor is corrected in the time axis, so that the wow in the reproducing sub-code synchronization signal SCOR can be removed and a sub-code synchronization signal GRSCOR in synchronization with the PCM data read from the DRAM 23 can be generated based on the read-out clock signal RFCK with a higher accuracy.
A match detection circuit 33 is provided to detect a match between the reproducing sub-code synchronization signal SCOR and the counter output of the inner circumference counter 29. For example, when there are two consecutive matches, a match detection signal GSS may be output. When the match detection signal GSS is sent, that is, when the reproducing sub-code synchronization signal SCOR and the counter output of the inner circumference counter 29 are consecutively matched two times, the reproducing sub-code synchronization signal GRSCOR is generated and output. As a result, an erroneous reproducing sub-code synchronization signal generated due to a scratch on the disk can be excluded and the reproducing sub-code synchronization signal GRSCOR of the optical disk player can be identified.
In the aforementioned optical disk player, the sub-code data obtained from the disk is temporarily stored in the memory, and then, the data read from the memory is finally selected by using the reproducing sub-code synchronization signal, so that the data can be reproduced by ensuring the data continuity without the sound discontinuity. Although the data is stable in a jitter environment causing vibration, a disadvantage of the conventional optical disk player is that the conventional optical disk player has a complex hardware construction.
Therefore, a need exists for a CD player with a minimum amount of hardware construction which is capable of reproducing data without sound discontinuity even in a jitter environment.